The present invention relates to a fly-back transformer which is used for supplying a DC high-voltage for example, to a cathode ray tube of a TV receiver or the like, and relates more particularly to a fly-back transformer which is improved in having a small ringing ratio.
Generally, the fly-back transformer includes a primary winding as an input winding, a secondary winding as a high-voltage output winding, and a tertiary winding for drawing out signals such as AFC, AGC, etc., and a secondary B power source. The windings are wound for magnetic coupling therebetween, said primary winding and tertiary winding being particularly closely coupled with each other. In the fly-back transformer having the above construction, it is desirable to make the ringing ratio small for efficient operation. As shown in FIG. 1 illustrating a high voltage pulse induced at the secondary side of a fly-back transformer, when for example, a fifth tuning is taken, the ringing ratio Rr is the ratio of the first wave crest value B of the ringing, and the sum A of a shot pulse wave crest value and the ringing wave crest value B, expressed as a percentage.Iadd.: .Iaddend.Rr=(B/A).times.100(%). In conventional fly-back transformers, the resonance circuit of the leakage inductance and the stray capacity of the secondary winding is properly tuned to make the ringing ratio smaller. In such transformers, however, since the ringing and shot pulses change in association with each other, it is extremely difficult to make adjustments. Furthermore, since the wave crest value of the shot pulse is made smaller at the same time, even if the wave crest value of the ringing is made to become smaller than a certain value, improvement of the ringing ratio is undesirably limited.